I've been trying to upgrade my tariff (sim only) every day for the last week and keep getting the "Oops, something's gone wrong!" message. I have tried to do this in previous months, had the same problem and gave up. This month I thought I would try again as I assumed it would have been fixed. No doubt the 'solution' will be to call customer services but I am reluctant to spend ages on the phone going through security questions etc when it's something that could be easily done in a few minutes online ... if only the website ever actually worked properly. As the main point of the 30 day rolling contract is to have the flexibility to change the tariff I was hoping that this might one day be fixed?!? Or maybe I just have unrealistic expectations!